Well, from a Mom with a little guy that has been to the doctor now twice for chronic bloody noses . . . I can relate. My son gets bloody noses that cover his whole face with blood . . . it is a little freaky. And he was getting them frequently. Turns out, he has seasonal allergies. He was rubbing and picking and scratching, etc. until he made large wounds in his nose called "turbinates". I didn't realize he had allergies, to be honest. (he just turned 5) but we've had a really bad year for them. So . . . he takes over the counter allergy medicine (claritan) and then we went through a week of a nasal spray so those wounds could heal. Bleeds stopped. I stopped the allergy medicine as Spring allergies should be over . . . no. Bloody noses started again! Back on the medicine for a bit longer. SO . .. when in doubt, call the doc!!
I think Sandman gives excellent advice too! We do the Vaseline in the winter with my older son who tends to get them when our furnace is on. (his aren't quite like my younger son . . . which can be like Helter Skelter)
I was told that bloody noses are hereditary. Either parent have them? good luck
Good question for a doctor. I'm not one, but one cause of nose bleeds is a very dry climate. You are in a area that probably would fit that description. Something that can help is a humidifier at night. Also a little Vaseline on a swab and rotated inside the nose will really help. The not breathing at night could be due to allergies - lots of over the counter stuff for that. Also, the nose strips that you put on the outside of the nose to open up the nose really work well. When ever we go to the high sierras (very dry) we use those and they do make a big difference.
Since this seems to only happen at summer, I am guessing that the dryness is a big factor.